Many materials used in the cosmetics and personal care product industries are unstable in the presence of sunlight. These ingredients are photolabile or ultra violet (UV) labile in that absorbed solar radiation causes degradation of these ingredients. This, in turn, can affect both the activity of the ingredient and the color of products into which these ingredients are incorporated.
This discoloration effect is particularly pronounced when UV-labile materials are dissolved in processing to form transparent or translucent products. Dissolution of such materials is preferred in the production of a transparent or translucent product in order to avoid unsightly specks of the material in the finished product. However, dissolution increases the surface area of the UV-labile material. Generally, the greater the surface area of such material, the greater the rate of photodegradation.
Clear fatty acid-based compositions typically discolor when exposed to sunlight because of the auto-oxidation of fatty acids. This discoloration is accelerated when phenol group-containing compounds, and particularly anti-microbial agents such as Triclosan are present because the alkaline pH of the soap and any polar solvents shift the UV spectrum of the Triclosan. This shift causes the Triclosan to absorb more solar UV energy (290-400.sub.nm), thereby increasing the rate of discoloration of the soap bar.
Typically, this discoloration effect is not seen in opaque products because it is not necessary to dissolve photolabile materials when preparing an opaque product. Simple physical mixing is sufficient for production of an opaque product.
Antioxidants and metal chelators have been used to combat color degradation due to auto-oxidation. For example, U.S. Pat. No. 4,469,338 describes the use of sodium metabisulfite, sodium sulfite, potassium bisulfite, sodium hydrosulfite, and potassium metabisulfite in combination with citric acid, sodium citrate or potassium citrate in sodium and triethanolamine salts to prevent color degradation. U.S. Pat. No. 3,793,214 describes the direct neutralization of saturated fatty acids with caustic soda and alkanolamine, and European Patent No. 0335026 describes the use of alkanolamine alkalines to achieve and maintain the clarity of transparent soaps. However, results have not been fully satisfactory.
The present inventors have discovered that photostable organic UV-absorbers are effective in maintaining the photostability of fatty acid-based compositions which contain phenol group-containing compounds and particularly in maintaining the clarity of non-opaque soaps containing phenolic compounds.